Were there mammalian pursuit predators in the tertiary? Dances with wolf avatars

Fast-running, long-legged pursuit carnivores are familiar members of the present-day ecosystem, and it has been assumed that extinct large predators took similar ecomorphological roles (i.e., were wolf avatars) in past faunas. While these fossil taxa may also have been meat-specialists, we present evidence from limb morphology to show that there was no modern type of pursuit predator until the latest Tertiary. In contrast, ungulates evolved longer legs similar to those of present-day cursorial taxa by the middle Tertiary, some 20 million years earlier. These data suggest the need for the reevaluation of many classical evolutionary stories, not only about assignation of fossil taxa to a wolf-like mode of predatory behavior, but also to issues such as the coevolution of long legs and fast running speeds between predator and prey, and even the implicit assumption that cursorial morphologies are primarily an adaptation for speed. We conclude that evolutionary change in ungulate limb morphologies represents an adaptation to decrease transport costs in association with Tertiary climatic changes and that the present-day predation mode of long distance pursuit is a Plio-Pleistocene phenomenon, related to the development of colder and more arid climates.     

On the origins of birds: the sequence of character acquisition in the evolution of avian flight

Assessment of competing theories for the evolution of avian flight is problematic, and tends to rest too heavily on reconstruction of the mode of life of one or a few specimens representing still fewer species. A more powerful method is to compare the sequence of character acquisition predicted by the various theories with the empirical sequence provided by cladistic phylogeny. Arboreal and cursorial theories incorrectly predict the sequence of character acquisition for several key features of avian evolution. We propose an alternative ''pouncing proavis'' model for the evolution of flight. As well as being both biologically and evolutionarily plausible, the pouncing proavis model correctly predicts the evolutionary sequence of all five key features marking the evolution of birds.     

Tuataras and salamanders show that walking and running mechanics are ancient features of tetrapod locomotion

The lumbering locomotor behaviours of tuataras and salamanders are the best examples of quadrupedal locomotion of early terrestrial vertebrates. We show they use the same walking (out-of-phase) and running (in-phase) patterns of external mechanical energy fluctuations of the centre-of-mass known in fast moving (cursorial) animals. Thus, walking and running centre-of-mass mechanics have been a feature of tetrapods since quadrupedal locomotion emerged over 400 million years ago. When walking, these sprawling animals save external mechanical energy with the same pendular effectiveness observed in cursorial animals. However, unlike cursorial animals (that change footfall patterns and mechanics with speed), tuataras and salamanders use only diagonal couplet gaits and indifferently change from walking to running mechanics with no significant change in total mechanical energy. Thus, the change from walking to running is not related to speed and the advantage of walking versus running is unclear. Furthermore, lumbering mechanics in primitive tetrapods is reflected in having total mechanical energy driven by potential energy (rather than kinetic energy as in cursorial animals) and relative centre-of-mass displacements an order of magnitude greater than cursorial animals. Thus, large vertical displacements associated with lumbering locomotion in primitive tetrapods may preclude their ability to increase speed.     

辽宁北票尾羽龙(Caudipteryx)一新种

１９９８年夏,中国科学院古脊椎动物与古人类研究所辽西野外考察队在北票上园张家沟采集到一块保存相当完整的、属于尾羽龙的头后骨架。该材料被订立一新种,对尾羽龙的已知特征作了重要的补充和修订。本文是对这一新材料的初步记述,并简单讨论了尾羽龙的系统位置和习性。 尾羽龙科（新科）Ｃａｕｄｉｐｔｅｒｉｄａｅ ｆａｍ． ｎｏｖ． 尾羽龙属 Ｃａｕｄｉｐｔｅｒｙｘ Ｊｉ ｅｔ ａｌ． １９９８ 董氏尾羽龙（新种） Ｃａｕｄｉｐｔｅｒｙｘ ｄｏｎｇｉ ｓｐ． ｎｏｖ． （图１～３;图版Ｉ～Ｖ） 词源种名谨献给我国杰出的恐龙学家董…     

IS MOM IN CHARGE? IMPLICATIONS OF RESOURCE PROVISIONING ON THE EVOLUTION OF THE PLACENTA

The Trexler–DeAngelis model shows that placentas are most likely to evolve in environments with consistent, high levels of resource availability. An assumption imperative to the model is that placental species abort embryos in low food conditions. However, a previous experimental test of this assumption using the northern clade of Poeciliopsis showed no evidence for abortion. To distinguish between the alternatives that placental species either sacrifice body condition to maintain reproduction when resources are restricted, or that the previously documented pattern of resource allocation is a function of other life‐history correlates of placentation rather than placentation alone, we perform a similar experiment on the southern clade of Poeciliopsis. The southern clade has the opposite relationship between life‐history traits and placentation as seen in the northern clade. Our results mirror those from the northern clade, indicating that reproductive mode, rather than life history, dictates the pattern of resource allocation. These results add to the difficulties of explaining placental evolution within the constraints of the Trexler–DeAngelis model by restricting the range of resource conditions in which placental species can outcompete nonplacental species. They also lend support to hypotheses that suggest parent–offspring conflict in utero drives the evolution of the placenta.     

CONTINUING THE DEFINITION OF DEATH DEBATE: THE REPORT OF THE PRESIDENT'S COUNCIL ON BIOETHICS ON CONTROVERSIES IN THE DETERMINATION OF DEATH

The President's Council on Bioethics has recently released a report supportive of the continued use of brain death as a criterion for human death. The Council's conclusions were based on a conception of life that stressed external work as the fundamental marker of organismic life. With respect to human life, it is spontaneous respiration in particular that indicates an ability to interact with the external environment, and so indicates the presence of life. Conversely, irreversible apnoea marks an inability to carry out the necessary work of life, an inability which the Council considers an indicator of death. This conception has been conceived to circumvent criticisms of the previous model of loss of somatic integration, a model the Council admits that, in the presence of evidence of continuing functional integration in brain dead patients, was looking less than convincing. Nevertheless, by focusing on external work and ignoring the more essential work of integrative unity, the Council's conception of the nature of life is untenable, and of no assistance in supporting a relation of equivalence between the concepts of brain death and death. Consequently, the Council's conclusions do little to advance the definition of death debate, a potentially intractable debate that may necessitate the investigation of alternate ethical justifications for organ harvesting.     

头足类若干结构的形态比较

本文首次系统观察分析比较了中国近海头足类的肉鳍、平衡器、齿舌和漏斗器,并参考世界代表性种类和古生头足类的文献和图,全面研究了这些结构形态的式型和亚型,探讨了它们与生活方式和演化的相互关系。     

THE COMPONENTS OF KIN COMPETITION

It is well known that competition among kin alters the rate and often the direction of evolution in subdivided populations. Yet much remains unclear about the ecological and demographic causes of kin competition, or what role life cycle plays in promoting or ameliorating its effects. Using the multilevel Price equation, I derive a general equation for evolution in structured populations under an arbitrary intensity of kin competition. This equation partitions the effects of selection and demography, and recovers numerous previous models as special cases. I quantify the degree of kin competition, α, which explicitly depends on life cycle. I show how life cycle and demographic assumptions can be incorporated into kin selection models via α, revealing life cycles that are more or less permissive of altruism. As an example, I give closed‐form results for Hamilton's rule in a three‐stage life cycle. Although results are sensitive to life cycle in general, I identify three demographic conditions that give life cycle invariant results. Under the infinite island model, α is a function of the scale of density regulation and dispersal rate, effectively disentangling these two phenomena. Population viscosity per se does not impede kin selection.     

PALAEOECOLOGY OF THE GRAPTOLITHINA, AN EXTINCT CLASS OF THE PHYLUM HEMICHORDATA

1. Whatever heirarchical system of classifying graptolites is adopted, perhaps even raising them to the rank of phylum, the hemichordates including Rhabdopleura and Cephalodiscus remain their closest relatives. 2. Benthonic graptolites preceded and outlasted the planktonic graptolites which exhibited spectacular morphological changes related to a change to a holoplanktonic mode of life and a probable hermaphroditism. 3. The resorption of the narrow-end of the larval skeleton (prosicular cauda) enabled the construction by an outer layer of secreting tissue (extrathecal tissue) of a hollow nema, the dark hollow rod which supported gas-filled tissue and which in turn conferred buoyancy on the colony. 4. The nema provided access to the exterior of the colony for extrathecal tissue which began to strengthen the outside of the prosicular and metasicular parts of the larval skeleton with laminated cortical deposits before the first non-sicular individual of the colony was budded. 5. Attachment of the larval stage in those graptolites having a basal disc or ‘roots’ was by the first-formed extrathecal tissue through a resorbed cauda. 6. Initial attachment of the larval stage in certain encrusting graptolites such as Idiotubus may have been by a larval individual lacking any scleroprotein periderm as a skeletal sheath. 7. After initial attachment the extrathecal tissue continued to secrete additional layers of cortical tissue mostly for the purposes of strengthening the colony. 8. Feeding in graptolites was by ciliated lophophore often positioned so as to take maximum advantage of currents flowing from the dorsal to the ventral side of the colony, for example in Dictyonema and Monograptus. 9. The main function of the nema, particularly of those nemata bearing vanes, was as a support for vacuolated tissue which imparted a holoplanktonic mode of life to planktonic (sensu Zato) graptolites. 10. Attachment of colonies (rhabdosomes) as groups of colonies (synrhabdosomes) was by the extrathecal tissue issuing from the tips of the nemata: such associations were probably sexual rather than for reasons of buoyancy. 11. Attachment of planktonic graptolites to floating algal fronds is an unnecessary hypothesis. Although an undoubted occurrence of graptolites in rocks containing large quantities of carbonaceous matter is beyond dispute, the plant or animal nature of this material has never been established. A symbiotic relationship of planktonic graptolites with a marine, formless alga, perhaps involving the extrathecal tissue, remains a possibility. 12. Although different species may have lived at different depths, the full vertical range of the holoplanktonic graptolites was probably small. The evidence advanced for depth zonation is considered inadequate. 13. Planktonic graptolites were essentially tropical to temperate in distribution with the bulk of the species and individuals in the former environment. 14. Automobility of graptolite rhabdosomes was an unlikely mechanism and does not readily account for the morphology and distribution of the graptolites. 15. Most planktonic graptolites were suspended beneath a nema coated in extrathecal, vacuolated (gas-filled) tissue: changes of position in the water were by passive response to ocean currents. 16. The nature of the graptolite zooid is considered unsolved, although it may have been essentially like that of the extant Rhabdopleura in having paired lophophores. 17. It is possible that a modified pre-oral lobe was capable of secreting both fusellar (inner) and cortical (outer) layers of the periderm. 18. The extrathecal tissue itself would in that case have been derived both from the nemal tube and the thecal individuals.     

Guild mobility affects spider diversity: Links between foraging behavior and sensitivity to adjacent vegetation structure

The movement patterns of species may affect their susceptibility to modified habitat structure. It is likely that sedentary species perceive habitat features at smaller spatial extents compared to mobile species, but there is a lack of experimental research on the effects of fine-scale habitat characteristics on organisms of differing mobility. Spiders display two basic mobility levels based on foraging behavior: web-building species are restricted to specific sites whereas active hunters are mobile. We collected spiders inhabiting sagebrush shrubs with a structurally enhanced, unmodified, or removed understory, to examine (1) whether habitat structure in the immediate vicinity of shrubs affected cursorial and web spiders differently in terms of abundance and species richness and (2) which genera most contributed to changes in community composition. Shrubs without understory had reduced cursorial spider densities and species richness compared to shrubs with added and unmodified understories, whereas web spiders lacked significant responses to treatments. Community-level differences based on relative abundance of genera were detected in cursorial spiders but not in web spiders, despite a strong contribution of the web-building genus Theridion to community dissimilarities. Our results support the hypothesis that sedentary organisms may be sensitive to contiguous habitat at finer spatial scales than cursorial organisms, and highlight the risks associated with only collecting local habitat information when studying mobile species.     

Effects of subsidized spiders on coastal food webs in the Baltic Sea area

The aim of this study was to examine top-down effects of cursorial spiders in subsidized coastal food webs. Top-down effects were examined by selectively removing cursorial spiders, mainly wolf spiders, from small islands (26–1834 m²) during 2004–2007. The removal success varied among islands and years, and spider densities were reduced by 30–65%. To examine treatment effects, arthropods were sampled using a vacuum sampling device at three occasions each summer. The densities of other arthropod predators, especially web spiders and carabids, were higher on islands where cursorial spiders had been removed compared to control islands. This treatment effect probably occurred through a combination of competitive release and reduced intraguild predation from cursorial spiders. No treatment effects were found on herbivore or detritivore densities and plant biomass. This lack of effect may either be because spiders indeed have fairly weak effects on herbivore and detritivore densities on Baltic shorelines or that the removal success of spiders was insufficient for observing such effects. Treatment effects may also be weak because negative effects exerted by spiders on herbivore and detritivore populations were balanced by increased predation by insect predators.     

青藏高原东缘61种常见木本植物种子萌发特性及其与生活史的关联

为了评价亚高山地带木本植物种子萌发对策及其与生活史关联, 该文对青藏高原东缘61种常见木本植物的种子萌发特征以及种子萌发与种子大小、扩散方式、海拔及生境的关系进行了调查分析。结果表明: 1) 61种植物的种子萌发率呈现偏斜、双峰分布。6种植物(9.8%)的种子萌发率大于80%, 13种(21.3%)的萌发率在60%~80%之间, 9种(14.8%)的萌发率在40%~60%之间, 8种(13.1%)的萌发率在20%~40%之间, 25种(41%)的萌发率小于20%, 其中8种植物的种子萌发率为零, 显示了该生境中木本植物的种子以休眠、低萌发率或连续稳定的萌发对策占优势, 以避免不利的环境因素。2)种子扩散方式是决定61种木本植物种间萌发率变异(R² = 24.1%, p < 0.001) 和萌发开始时间变异(R ²= 21.3%, p < 0.01) 的主要因素; 种子大小、母体植株的海拔和生境对种子萌发率和萌发开始时间几乎没有影响(p > 0.05); 风扩散的种子比脊椎动物扩散和无助扩散的种子有更高的萌发率(F = 9.219, p < 0.001) 和较早的萌发开始时间(F = 6.772, p < 0.01)。说明植物生活史特征如种子萌发与扩散方式之间存在固有而紧密的联系, 扩散能力强的种子(如风扩散)由于能散布到较远而空旷的生境, 可能避免了各种有害因素或个体竞争, 因而种子以较强的萌发能力进行拓殖; 扩散能力弱的种子(如无助扩散)由于其散布距离较近, 种子以休眠或降低萌发的方式来避免个体或同胞竞争以及各种有害因素, 以获得最大的生态利益并确保物种延续。     

Patch quality and connectivity influence spatial dynamics in a dune wolfspider

The spatial population dynamics of the wolfspider Pardosa monticola, inhabiting patchily distributed grasslands in the Flemish coastal dunes of Belgium and Northern France were investigated with incidence function models using field survey data from 1998 and 2000. Vegetation height and patch size were related to habitat quality. Mark-recapture experiments revealed maximum cursorial dispersal distances of 280 m for moss dunes and 185 m for higher dune grassland. Higher shrub vegetation appeared to be dispersal barriers. These habitat-dependant cursorial distances and the theoretically estimated ballooning distance were included with patch distances into a connectivity index for both dispersal modes. Forward multiple regression indicated that patch occurrence was influenced by habitat quality and ballooning connectivity. Habitat quality and cursorial connectivity explained patterns in short-term colonisation. Extinction appeared to be stochastic and not related to habitat quality and connectivity. Genetic differentiation and variability was low. The discrepancy between the estimated low dispersal capacity and the indirect estimate of gene flow ( F(ST)) indicates that historical population dynamics and/or historical ballooning dispersal influence the genetic structure in this species.     

Distinct feeding strategies of generalist and specialist spiders

1. Feeding behaviour of generalist and specialist predators is determined by a variety of trophic adaptations. Specialised prey‐capture adaptations allow specialists to catch relatively large prey on a regular basis. As a result, specialists might be adapted to exploit each item of prey more thoroughly than do generalists. 2. It was expected that obligatory specialist cursorial spiders would feed less frequently than generalists but for a longer time and, thus, that their foraging pause would be longer. First, the feeding frequencies of three generalist spider species (Cybaeodamus taim, Harpactea hombergi, Hersiliola sternbergsi) were compared with those three phylogenetically related specialist species: myrmecophagous Zodarion rubidum, and araneophagous Nops aff. variabilis and Palpimanus orientalis. 3. Generalists captured more prey, exploited each item of prey for a significantly shorter time, and had a shorter foraging pause than was the case for specialists. Generalists also gained significantly less relative amount of prey mass than did specialists. 4. Second, the study compared the prey DNA degradation rate in the gut of generalists and specialists by means of PCR. The degradation rate was not significantly different between specialists and generalists: the detectability half‐life was estimated to exist for 14.3 days after feeding. 5. This study shows that the feeding strategies of cursorial generalist and obligatory specialist spiders are different. Obligatory specialists have evolved a feeding strategy that is based on thorough exploitation of a few large prey, whereas generalists have evolved a strategy that is based on short exploitation of multiple small items of prey.     

EXPERIMENTAL MODIFICATION OF THE MORPHOGENETIC BEHAVIOR OF THE ISOLATED SUB-APICAL CELL OF THE APEX OF SPHACELARIA CIRROSA (PHAEOPHYCEAE)1

Experimental isolation of the terminal cells of the apex of Sphacelaria cirrosa (Roth) C. Agardh shows that the isolated apical cell retains a self-maintained mode of functioning. The isolated sub-apical cell, however, gives rise to a newly-formed axis after undergoing a different type of developmental sequence. An experimental scheme allowing one to defer isolation of the sub-apical cell after killing the apical cell shows that the maintenance, for a few hours only, of connections with subjacent cells is sufficient to induce an apical type mode of functioning in the sub-apical cell. The sequential analysis of the first cytological events in this phenomenon allows one to relate this modification of the morphogenetic program to a functional and polarized arrangement of organelles within the cell reconstituting the apical. The morphogenetic program is characterized by a migration of the nucleus to a distal position prior to an asymmetrical mitosis characteristic of the apical mode of functioning.     

Cursorial spiders retard initial aphid population growth at low densities in winter wheat

Generalist predators contribute to pest suppression in agroecosystems. Spider communities, which form a substantial fraction of the generalist predator fauna in arable land, are characterized by two functional groups: web-building and cursorial (non-web-building) species. We investigated the relative impact of these two functional groups on a common pest (Sitobion avenae, Aphididae) in wheat by combining a molecular technique that revealed species-specific aphid consumption rates with a factorial field experiment that analyzed the impact, separately and together, of equal densities of these two spider functional groups on aphid population growth. Only cursorial spiders retarded aphid population growth in our cage experiment, but this effect was limited to the initial aphid-population growth period and low-to-intermediate aphid densities. The molecular analysis, which used aphid-specific primers to detect aphid DNA in predator species, detected the highest proportion of aphid-consuming individuals in two cursorial spiders: the foliage-dwelling Xysticus cristatus (Thomisidae) and the ground-active Pardosa palustris (Lycosidae). The results suggest that manipulating the community composition in favour of pest-consuming functional groups may be more important for improving biological control than fostering predator biodiversity per se. Agricultural management practices that specifically foster effective species or functional groups (e.g. mulching for cursorial spiders) should receive more attention in low-pesticide farming systems.     

IMMORTALITY, HUMAN NATURE, THE VALUE OF LIFE AND THE VALUE OF LIFE EXTENSION

The emerging discourse concerning the desirability of intervention in senescence to achieve radical life extension for persons has featured some striking blurring in traditional liberal and conservative commitments and positions. This affords an opportunity for re‐evaluation of these same. The canonical conservative view of the intrinsic value of life is re‐examined and found primarily to involve a denial of human prerogative, rather than an active underwriting of the value of life extension. A critique is offered of an attempted argument against aging intervention from a proto‐conservative worry about a purported threat to human nature. Immortality is found to be a red herring, but a revealing one. Further, the classic liberal view is examined and found wanting in terms of the gravity of its own commitment to, and fullness of its account of the value of life, and the value of life extension. An analysis of the liberal conception of personhood is proposed that both defines persons necessarily as processes, and demonstrates the inalienable quality of the value of life extension to persons so defined.     

A dynamic similarity hypothesis for the gaits of quadrupedal mammals

The dynamic similarity hypothesis postulates that different mammals move in a dynamically similar fashion whenever they travel at speeds that give them equal values of a dimensionless parameter, the Froude number. Thus, given information about one species, it could be possible to predict for others relationships between size, speed and features of gait such as stride length, duty factor, the phase relationships of the feet and the patterns of force exerted on the ground.
Data for a diverse sample of mammals have been used to test the hypothesis. It is found to be tenable in many cases when comparisons are confined to quadrupedal mammals of the type described by Jenkins (1971) as "cursorial". Most mammals of mass greater than 5 kg are of this type. Although the hypothesis applies less successfully to comparisons between cursorial and non-cursorial mammals it is shown to be a reasonable approximation even for such comparisons and for comparisons between quadrupedal mammals and bipedal mammals and birds.     

LIFE IN THE FAST LANE: THE LIFE HISTORY OF HARBOR PORPOISES FROM THE GULF OF MAINE

We describe the life history of harbor porpoises in the Gulf of Maine by examining 239 animals killed in gill net fisheries and comparing these findings with the results of previous studies from the Bay of Fundy. Most female porpoises matured at age three and became pregnant each year thereafter. Reproduction was strictly seasonal, with ovulation, conception, and parturition occurring in the spring and early summer. The oldest specimen in the sample was 17 yr of age, but most individuals were younger than 12. The findings are similar to those of earlier studies from the Bay of Fundy and support the hypothesis that these animals form a single population. Harbor porpoises represent one end of a continuum of odontocete life histories that spans a wide diversity of strategies. In comparison with other, large odontocetes, harbor porpoises mature at an earlier age, reproduce more frequently, and live for shorter periods.